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1949
ARC SPOTLIGHT
413
A two-element, variable-focal-length lens system, which continuously focuses on the aperture, is used to project the desired spot sizes. This system consists of a 21/2-inch focal length, 2-inch diameter double convex pyrex lens, and an 18-inch focal length, 7-inch diameter planoconvex objective lens. A handle mounted on the side of the large lens carriage controls the variation of projected spot size. This handle may also be utilized to vary the angularity of the spotlight to maintain the spot on a moving act.
A specially designed linkage is provided to control the relative movement between the two lenses. The linkage properly adjusts, automatically, the distance between the lenses as they are moved toward or from the light source. A clear-cut spot is created at any po
LENS
POSITIONING RIBBON
Fig. 4 — Lens optical system.
sition. A spot-sharpness focusing control slightly changes the relative position of the lenses, to compensate for variation of projection distances.
The aperture plate, upon which the lens optical system is focused, has three positions of use, and is actuated by a conveniently located handle. In position 1, a 1 V4-inch-diameter hole emits the light, and will allow a variation in spot size from a small spot to a stage flood. From minimum to maximum positions, the spot diameter will increase seven times. Position 2 is a 3/4-inch-diameter hole, used only for a small head spot. Position 3 can be used as a dowser. A quick flip of the aperture handle and any one of these positions can be obtained instantaneously. As an example of spot-size variation for a 60-foot throw, the P/Vinch-diameter aperture will handle spot sizes from 4y2 feet to 32 feet in diameter. With the 3/4-inch aperture a 2l/r foot head spot can be obtained.